1. Field of the Invention
The present invention relates to a wireless charging system which supplies electric power by utilizing a mutual interaction of electromagnetic induction.
2. Description of the Related Art
A charging system is configured to feed electric power from an electric power system to a secondary battery mounted to an electric moving vehicle or the like, thereby storing power in the secondary battery. One example of such charging systems is a wireless charging system in which the electric power system is not connected to the secondary battery in a wired manner. With regard to a technique relating to the wireless charging system, there is known one including a wiring (primary coil) on a transmitter unit side and a wiring (secondary coil) on a receiver unit side which have a structure in which an electric wire is wound in a flattened manner, and flat plate-like magnetic cores around which the two wirings are wound, respectively. This technique, for example, is described in JP-4356844-B. A so-called wired charging system requires an operation with which a driver of the electric moving vehicle gets off the vehicle on a case-by-case basis and carries out connection to a plug for electric power feeding installed in a charging station or the like, and so forth. However, if the wireless charging system is used, then the electric power can be supplied from the transmitter unit including the electric power system to the receiver unit including the secondary battery by utilizing a mutual interaction of electromagnetic induction. As a result, an operation accompanied by the getting on and off of the driver becomes unnecessary and so his or her convenience is enhanced. A problem with this kind of technique, however, is that the charging efficiency is reduced because the wireless style is used between the transmitter unit and the receiver unit.
To increase the charging efficiency of the wireless charging system, a shaft center of the transmitter unit (a shaft center of the primary coil) and a shaft center of the receiver unit (a shaft center of the secondary coil) are preferably aligned with each other as much as possible. The reason for this is because if the shaft centers of the transmitter unit and the receiver unit are different from each other (imperfect alignment), then, a part of magnetic field lines generated by the transmitter unit does not interlink the receiver unit, and thus electric power feeding efficiency is reduced in some cases. With regard to a technique which was made in the light of this respect, there is known one with which the transmitter unit and the receiver unit are aligned with each other based on the electric power change either in the primary coil or in the secondary coil due to the induced electromagnetic force, whereby the shaft centers of the transmitter unit and the receiver unit are tried to make automatically close to each other without requiring a special operating technique. This technique, for example, is described in JP-H8-265992-A.
In addition, the following technique is also known. A primary core having a protrusion portion made of a soft magnetic material and passing through the primary coil is provided in the transmitter unit, and a secondary core having a protrusion portion made of a soft magnetic material and passing through the secondary coil is provided in the receiver unit. Therefore, even when the primary core and the secondary core come in contact with each other in a state of being slightly misaligned with each other, the stable electric power supply is tried to be carried out while the shock when the primary core and the secondary core come in contact with each other is relaxed. This technique, for example, is described in JP-2011-151351-A.